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RESEARCH ARTICLE
Contents Vol 56(8)

In vitro degradability of feed proteins in the rumen: use of non-rumen proteases

M. Aslam Mirza A C and E. L. Miller B
+ Author Affiliations
- Author Affiliations

A Institute of Animal Nutrition and Feed Technology, University of Agriculture, Faisalabad, Pakistan.

B Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge, United Kingdom CB3 OES.

C Corresponding author. Email: mmirza@nsac.ns.ca

Australian Journal of Agricultural Research 56(8) 797-801 https://doi.org/10.1071/AR04111
Submitted: 17 May 2004  Accepted: 14 June 2005   Published: 25 August 2005

Abstract

Various feed proteins were incubated independently with bacterial protease from Streptomyces griseus (SGP), papain (Corica papaya), and ficin (Ficus glabrata) in a simple laboratory assay to predict ruminal protein degradability. The estimates obtained from in vitro assays were compared with those obtained from an in situ analysis using synthetic fibre bags. The rate and extent of degradation in vitro using proteases from non-rumen sources differed among substrates used. A high correlation coefficient (r2 = 0.99) was observed between N-degradability from the in vitro method using SGP and in situ estimates when soybean meal was the substrate. Soybean meal nitrogen (N) was almost completely hydrolysed (0.99) in vitro. The correlation coefficients were low and variable with assays using other enzymes. The correlation coefficient was also high (r2 = 0.77–0.84) with in vitro methods using either SGP, papain, or ficin when incubated with fish meal. The N disappearance from barley in vitro was slow to moderate. The ‘b’ estimate of barley obtained with the in vitro assay was significantly (P < 0.01) lower than that observed in situ. Slower proteolysis observed in barley may possibly be linked to poor accessibility of structural proteins rather than the degradability of N per se. None of the enzymes could rank barley in the same order as the in situ method.

Additional keywords: protein degradation, bacterial protease, papain, ficin.


Acknowledgments

This study was sponsored by the Cambridge Commonwealth Trust in the form of a scholarship provided to the first author. The assistance of Dr Alan Fredeen, Haley Institute of Animal Science and Aquaculture, NSAC, Truro, NS, in reading the manuscript and giving useful suggestions is gratefully acknowledged.


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